Projected beam-type smoke detectors are known and can be useful additions to regional monitoring systems, such as fire monitoring and alarm systems. Such detectors are disclosed, for example, in U.S. Pat. No. 6,822,216 B1 issued Nov. 23, 2004 entitled “Obscuration Detector”. The '216 patent is assigned to the assignee hereof and incorporated by reference herein.
Detectors of the type noted above could be incorporated into monitoring systems such as disclosed in U.S. Pat. No. 6,691,172 B1 issued Feb. 10, 2004 and entitled “Communication System for Defining a Variable Group of Processors for Receiving a Transmitted Communication”. The '172 patent is assigned to the assignee hereof and incorporated by reference herein.
Detector sensitivity is affected by beam travel distance in such detectors. It has been recognized that there is a need to establish a beam travel distance between a transmitter and a receiver of a projected beam-type detector on installation. Such distances can be manually measured at installation and a sensitivity parameter of the unit set accordingly.
It has also been recognized that where such detectors have a common housing for the transmitter and receiver, with the beam being reflected therebetween, that beam travel can be improperly interfered with by placing an obstruction having a reflective surface in the path of the beam.
There is thus a continuing need to more cost effectively carryout measurements of beam travel and to be able to recognize where interference with the beam has taken place. Preferably, such improved functionality could be automatically implemented using a transmitter and receiver present in such detectors to detect smoke.